Traveling wave electron discharge device having means exerting a radial force upon the envelope



Sept. 6, 1966 F. L. WASHBURN, JR 3,271,615

TRAVELING WAVE ELECTRON DISCHARGE DEVICE HAVING MEANS EXERTING A RADIAL FORCE UPON THE ENVELOPE Filed Aug. 25, 1961 4 Sheets-Sheet 1 Fig. 2

wnmzssss INVENTOR 994 (7% Frederick L. Woshburn,Jr. M [7 ATTORNEY Sept. 6, 1966 F. 1.. WASHBURN, JR

TRAVELING W ELECTRON DISCHARGE DEVICE HAVING MEANS EXERTI A RADIAL FOR Filed Aug. 25, 1961 v CE UPON THE ENVELOPE 4 Sheets-Sheet 2 Sept. 6, 1966 WASHBURN, JR 3,271,615

TRAVELING WAVE ELECTRON DISCHARGE DEVICE HAVING MEANS EXERTING A RADIAL FORCE UPON THE ENVELOPE Filed Aug. 25, 1961 4 Sheets-Sheet 3 Sept. 6, 1966 F. L. WASHBURN, JR 3,271,615

TRAVELING WAVE ELECTRON DISCHARGE DEVICE HAVING MEANS EXERTING A RADIAL FORGE UPON THE ENVELOPE Filed Aug. 23, 1961 4 Sheets-Sheet 4 Eli United States Patent 3,271,615 TRAVELING WAVE ELECTRUN DISCHARGE DE- VICE HAVING MEANS EXERTING A RADIAL FORCE UPUN THE ENVELQIPE Frederick L. Washhurn, .Irz, Round Bay, Md, assrgnor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. 23, 1961, Ser. No. 133,346 6 Claims. (Cl. SIS-35) This invention relates generally to electron discharge devices and more particularly to microwave tubes of the traveling-wave type.

Discharge devices of the class described herein generally comprise an elongated, evacuated envelope having means disposed at one end thereof for the productionand projection of an electron beam along a predetermined path and a slow-wave propagating means, usually comprising an electrical conductor in the form of a helix, for propagating electromagnetic waves along the length of the envelope in an interacting relationship with the electron beam. In relatively high powered tubes of this type, considerable heat is generated within the helix by beam interception and radio frequency losses and, as the temperature of the helix rises, so too does the resistance, with a resulting diminishment in the radio frequency power output of the tube. Further in some tubes this heating effect may be so great as to completely destroy the helix or other slow-wave structure.

It is therefore the principal object of this invention to produce improved means for the removal of heat from slow-wave propagating means of the helix type.

A further object of this invention is to provide improved means for supporting the slow-wave propagating structure within a traveling wave tube.

Another object of this invention is the provision of improved means for the procurement of an improved heat path through the helix support means located within the envelope of a traveling wave tube.

Another object of this invention is to provide improved means for conducting heat from the attenuator of the tube which attenuator is usually a part of the support rods.

Briefly, the present invention provides an electron discharge device of the type having a slow wave structure which is supported within an envelope through the use of at least one support member positioned between the slow wave structure and the envelope. In order to improve the heat transfer from the slow wave structure, compression means are supplied to the exterior of the envelope to provide better heat contact between the slow structure, the support members and the envelope.

The above and other objects are etfected by this invention as will be apparent, from the following description of several embodiments of the invention, when read in conjunction with the accompanying drawings in which like reference characters indicate like parts and in which:

FIGURE 1 is a side elevational view, partly in section and with certain parts being broken away, of a traveling wave tube embodying the present invention;

FIG. 1a is an enlarged fragmentary view showing a step in the production of the tube of FIG. 1;

FIG. 2 is a fragmentary transverse sectional view through the body portion of the device of FIG. 1 taken substantially along the line II-II of FIG. 1;

FIG. 3 is a side elevational view, partially in section and partially broken away, of a modification of the tube shown in FIG. 1 in accordance with the invention;

FIG. 4 is a fragmentary transverse sectional view, through the tubular body portion of the device of FIG. 3, taken along line IVIV of FIG. 3;

' FIG. 5 is a fragmentary transverse sectional view through a tube modification (of the transverse section constructed in accordance with a modification of the invention shown in FIG. 4); the section being taken transversely through the mid-portion of the tube;

FIG. 6 is a fragmentary transverse sectional view through a tube (of the transverse section constructed in accordance with a further modification of the invention shown in FIG. 4); the section being taken transversely through the mid-portion of the tube;

FIG. 7 is a side elevation view, partially in section, of a further modification of the tube shown in FIG. 1 in accordance with this invention;

FIG. 8 is a transverse sectional view of the initial assembly of the envelope and its interior components of the tube shown in FIG. 7; and

FIG. 9 is a transverse sectional view of the assembly shown in FIG. 8 with the envelope partially restored to its original circular configuration and with some deformation of the helix and before the final assembly shown in FIG. 7 has been made.

With specific reference to the embodiment illustrated in FIG. 1, the discharge device comprises an elongated, evacuated envelope 1 of suitable material such as copper or Monel metal. Disposed at one end of the tube and indicated generally by the reference character 3, is an electron beam source. This source comprises an elec tron emissive cathode 5, a focusing electrode 7, and an accelerating electrode 9. These elements are connected to suitable sources of voltage, which are not shown, and

collectively act to direct a beam of electrons centrally 1 along the axial length of the envelope 1 to the opposite end of the envelope wherein is located an electron collecting anode 11. The anode 11 is also connected to a suitable source of voltage which is not shown. A slowwave propagating means 17, for the propagation of radio frequency energy, is disposed centrally within the envelope 1 for a major portion of its axial length and is coaxial with and in an interacting relationship with a major portion of the electron beam. The propagating means comprises an electrical conductor, usually in the form of a helix, which helix may be single wound, crosswound, or bifilar-wound and may be of wire or tape in accordance with good engineering principles. Electromagnetic energy may be applied to the helix or slowwave propagating structure by means of a coaxial cable 21 which extends and is sealed through the side of the envelope, or by any other suitable electrical network. A second coaxial cable 22 may be provided at the opposite end of the helix for the removal of the radio frequency energy from the helix.

The slow-wave propagating means 17, comprising the helix, is supported within the envelope 1 by means of a plurality of supporting members 15 (FIG. 2) which are disposed along the axial length of the envelope for substantially the entire length of the helix. As shown in FIG. 2, these supporting members are substantially keystone in shape and are made of -a suitable heat conducting, electrical insulating ceramic such as alumina or beryllia. While three equally spaced keystone support members are shown in the drawing, this number is not critical and the number of members and their relative spacing about the helix may be varied as the individual case may require. The keystone shape provides several advantages over circular type support members. The keystone shape provides for greater contact area at both the helix and envelope ends of the supporting members. The shape also provides less dielectrical material in the immediate vicinity of the helix and hence lowers the dielectric loading in that area, as well as providing a mechanical structure which is superior to that of the circular rod.

In order to provide a more efficient heat conducting path between the helix 17, the keystone support members 15, and the outside envelope 1, means are provided exterior to the envelope to supply a radial compressive force to the outside wall of the envelope to insure a more rigid and tightly fitting assembly within the envelope. In its most rudimentary form, this compressive force is achieved by tightly wrapping a wire 19, of high tensile strength, around that portion of the envelope in which the helix is located. A more satisfactory means of supplying radial compressive stress to the envelope 1 is as follows. The envelope 1 is made of material having a relatively low coefiicient of thermal expansion, such as Monel metal. A wire 19 having a high tensile strength and a relatively high coefiicient of thermal expansion compared to the envelope material, for example austenitic stainless steel, is then tightly wound around that portion of the envelope 1 containing the helix 17. After this assembly is made, a brazing material 23 in wire form, for example eutectic silvercopper alloy, is also wound around the same portion of the envelope 1 so as to form overlying turns on the stainless steel wire (FIG. la). The entire assembly is then heated to a temperature above the melting point of the brazing material. At the elevated temperature, the stainless steel wire will expand to a greater extent than will the Monel envelope due to the differences in the coefficient of thermal expansion. This difference in expansion will create a space or gap between the wire and envelope into which the now molten brazing material will flow. Upon cooling, the stainless steel wire and the Monel envelope will attempt to return to their original size. However, due to the fact that a certain amount of brazing material has flowed into the space between the wire and the envelope, the stainless steel wire will not be able to fully return to its original size but rather will remain under tensile strain. The brazing material which is located between the stainless steel wire and the Monel envelope will act as a spacing element and Will ensure that the stainless steel Wire exerts a much greater compressive force on the assembled structure than was originally achieved by merely tension winding the wire around the envelope. Thus, the entire assembly is placed under a radial compressive force or stress which will insure good thermal contact between the helix 17, the support rods 15, and in turn, between the rods and the envelope 1. A good thermal path from the helix to the envelope to effect the removal of heat from the helix is thus formed.

In order to prevent the electron beam from spreading to such an extent that it would pass out of the interacting region and possibly intercept the slow-wave propagating means, it is necessary to provide some focusing means. Focusing in the present instance is provided by producing a magnetic field axially along the structure. This is achieved by providing a long angular solenoid 13 which surrounds the envelope for the entire length of the helix 17. To simplify the present drawing and description, the magnetic field producing solenoid 13 is only partially and schematically illustrated and its source of energization is not shown.

FIG. 6 discloses a modification of the invention in which the compression stress between the helix and the rods, and also between the rods and the outside envelope, is more readily obtained because the cross sectional area of the envelope wall has been decreased adjacent to the rods. An externally applied force, for example one applied by the binding wire, can then be more reliably applied to the system by deforming the envelope wall. As illustrated in FIG. 6, the outside surface of the envelope is of quasitriangular shape. The internal structure of the tube is the same as the embodiment shown in FIG. 1. One or more spacing means in the form of circular spacing members 25 are then placed axially along the fiat portions of the exterior wall of the envelope 1, and the abutting turns of stainless steel wire 19 and the overlying turns of brazing material 23 are then wound about tube and spacing members 25. The heating and cooling process is carried out as before. If the number of spacing members is made to equal the number of supporting members, and these elements are aligned one with the other as is shown in FIG. 6, it is readily seen that a stable structure is achieved in which the radial compressive force is concentrated on the supporting members 15. The stability of the structure may be further improved by cutting keyways in the inside of the envelope to contain the support rods.

In addition to the greater concentration of compressive stress, the structure of FIG. 6 possesses another advantage over that of the FIG. 1. After the brazing operation has been completed, the turns of steel Wire and the brazing material will form a continuous cylinder 27 surrounding both the envelope 1 and the spacing members 25. The continuous cylinder wall is achieved because of the attraction of the brazing material to the stainless steel wire. This attraction holds the brazing material to the wire and prevents it from falling through any small spaces which may exist between the abutting wires. This cylinder, along with the outside wall of the envelope 1 and the spacing members 25 will form axial tubular spaces or conduits 29 along the exterior Wall of the envelope for the length of the helix. These conduits 29 may be used to provide means along the exterior wall of the envelope 1 through which the cooling medium such as water may be circulated. This circulation may be achieved by means of a pump which is connected to a manifold means at each end of the conduits 29. The pump and manifold means have not been shown for the sake of simplicity.

Another modification of the invention is shown in FIGS. 3 and 4 of the drawing. In this embodiment one or more longitudinally extending recesses 39 are provided around the interior wall of the envelope 1. The number of these recesses is preferably equal to and in alignment with the number of supporting members 15. Conduits 31 are disposed, at least partially, within recesses 39 in thermal contact with the supporting members 15. As shown in FIG. 3, a cooling medium is circulated through the conduits 31 by means of a pump 33 which is connected to conduits 35 which are sealed through the envelope 1 and connected to conduits 31. The conduits 31, as illustrated in FIG. 4, are preferably made of a pliable, heat conducting material, for example, copper. Good thermal contact between the support members 15 and conduits 31 may be insured by subjecting the conduits to a fluid pressure of sufficient magnitude to cause deformation of the conduit walls into thermal engagement over a substantial area of the sides and bottom of the recesses and the end surface of the support members after the assembly of the tube has been made.

A further modification of the device illustrated by FIG. 4 is shown in FIG. 5. In this modification, cooling conduits 37 comprising tubular members of ceramic material having the same coeflicient of temperature expansion as that of the support members 15, preferably alumina or beryllia in the present example, are provided. These conduits are disposed along the axial length of the helix in thermal contacts with the support members 15 and the envelope wall. If it is desired to increase the thermal contact area between the conduit 37 and support rods 15, small amounts of brazing material 41, for example, eutectic silver-copper alloy, may be placed at the contact points between the conduit 37 and the support members 15. A suitable cooling fluid such as water is adapted to be circulated through the conduits 37 to remove the heat from the slow-wave propagating means by means of a pump, not shown, similar to that shown in FIG. 3.

Another modification of the invention is shown in FIGS. 7 through 9. This modification is particularly suitable for periodic permanent magnetic focusing in traveling wave tubes and utilizes iron magnetic pole pieces 43 exterior to the envelope 1 to replace the high tensile strength wire of the earlier embodiments for supplying the radial compressive force to the external wall of the envelope 1. It is important in this embodiment that a ,spect to the envelope 1.

thin wall envelope, preferably copper, is used. The helix 17 is preferably put in radial stress by deforming, as shown in FIG. 8, by means of some auxiliary mechanical device which has not been shown, the normally circular envelope to make it slightly triangular, square, or polygonal depending upon the number of support members utilized. This radial stress is achieved by using an envelope having an inside diameter slightly less than that which would just surround the helix and support rods if no envelope distortion were present. After the helix 17 and support members 15 have been inserted into the envelope, the auxiliary distorting device is removed allowing the envelope to attempt to restore itself to its prior circular form as is shown in FIG. 9. Because the envelope is thin walled, to allow sufficient initial distortion, it will not be capable of completely restoring itself to the original circular shape. The envelope 1 is then forced into a substantially circular cross sectional area by suitable external compression means, for example a series of adjustable circular clamps. The forcing of the envelope into a substantially circular cross section results in some slight physical deformation of the slow-wave structure as is shown in FIG. 9. It is this deformation which results in the radial stress existing between the helix and the support rods and in turn between the support rods and the outside envelope. Pole pieces 43 are then forced onto the envelope 1 to hold the envelope in its circular shape and retain the compressive stress on the structure. This technique will make the necessary firm contact between the helix 17 and the support members 15 and also be tween the support members and the envelope 1, and will ensure a good thermal conductive path between these elements. The magnetic pole pieces 43 may then be brazed to the envelope to provide improved thermal con tact between these two elements. The pole pieces 43 not only perform the usual function of shaping the magnetic field but also strengthen the envelope.

An alternative method of forcing the envelope 1 into a substantially circular cross-section is by forming the pole pieces 43 in two semi-circular segments having an inside diameter equal to that of the outside diameter of the undistorted envelope. The two pole segments may then be forced together by suitable means, e.g., an ordinary vise, and brazed at their mating edges to form unitary structures. This method will also cause some deformation of the helix 17 but will also achieve the desired thermal contacts between the components of the internal structure.

To increase the cooling effect, the pole pieces 43 are provided with flange portions 53 which act to support permanent magnets 47 in a spaced relationship with re- The pole pieces are also pro vided with a series of passageways 51 extending longitudinally through the flange portions 53. These passageways provide a flow path for a cooling medium and places the cooling medium in thermal contact with both the pole pieces and portions of the envelope wall. The cooling medium may be either liquid or gas and is supplied by suitable conduit, manifold, and circulating means which have not been shown.

The permanent magnets 47 are assembled alternately with the soft iron pole pieces 43 and provide the magnetic focusing for the tube.

While there have been shown and described what are at present considered to be the preferred embodiments of the invention, modifications thereto will readily occur to those skilled in the art. It is not desired, therefore, that the invention be limited to the specific arrangements shown and described and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

I claim as my invention:

1. A traveling wave electron discharge device comprising an envelope made of a deformable, metallic material,

means for generating and projecting an electron beam, means disposed for collecting said electron beam, wave propagating means disposed in an interacting relationship with said electron beam, a plurality of electrically insulating, heat conducting support members disposed between and abutting said envelope and said wave propagating means to position said wave propagating means in a spaced relationship with respect to said envelope, and annularly shaped members disposed about said envelope and having an inside diameter of such size so as to exert a radial compressive force on the outside Wall of said envelope whereby good thermal contact is achieved between said wave propagating means, support member, and envelope.

2. An electron discharge device comprising a metallic envelope, means for the production and projection of an electron beam, means disposed for the collection of said electron beam, means for the propagation of wave energy disposed within said envelope, said propagating means disposed in an interacting relationship with said electron beam, a plurality of beryllia support members disposed between and abutting said envelope and said wave propagating means, and means for supplying a radial compressive force to said envelope whereby there are provided good thermal contacts between said propagating means and said support members, and between said support members and said envelope.

3. A traveling wave electron discharge device comprising an envelope of a deformable, metallic material, means for generating and projecting an electron beam, means disposed to receive said electron beam, wave propagating means disposed in an interacting relationship with said electron beam, a plurality of electrically insulating, heat conducting members disposed between and abutting said envelope and said wave propagating means to position said wave propagating means in a spaced relationship with respect to said envelope, said envelope being stressed to tend to form a first configuration, and retaining means disposed about said envelope tending to form said envelope to a second configuration differing from said first configuration for establishing a radial force upon said envelope, said heat conducting members and said wave propagating means to thereby provide eificient thermal contacts between said envelope and said heat conducting members, and between said heat conducting members and said wave propagating means.

4. A traveling wave electron discharge device comprising a metallic envelope, means for generating and projecting an electron beam, means disposed to collect said electron beam, wave propagating means disposed in an interacting relationship with said electron beam, a plurality of electrically insulating, thermal conducting support members disposed between and abutting said envelope and said wave propagating means to position said wave propagating means in a spaced relationship with respect to said envelope, means for establishing a radial, inwardly directed force upon said envelope, said support members and said wave propagating means to insure eflicient thermal contacts between said envelope and said support members, and between said support members and said wave propagating means.

5. A traveling wave electron discharge device comprising an envelope, said envelope made of a deformable, metallic material and being stressed so as to tend to form a first configuration, means for generating and projecting a beam of electrons, means disposed to collect said beam of electrons, wave propagating means disposed in an interacting relationship with said beam of electrons, a plurality of electrically insulating, heat conducting support members disposed between and abutting said envelope and said wave propagating means to position said wave propagating means in a spaced relationship with respect to said envelope, and pole members located external to and about said envelope for directing lines of flux so as to focus said beam of electrons, said pole members having an annular configuration with an inside diameter of such size that said pole members tend to reshape said envelope to a second configuration different from said first configuration and to thereby establish a radial force upon said envelope, said support members and said wave propagating means whereby efficient thermal contacts are achieved between said wave propagating means, said support members, and said envelope.

6. A traveling wave electron discharge device as claimed in claim 5, wherein said pole members contain passageways to permit the flow of a cooling fiuid along said envelope, and means to circulate said cooling fluid through said passageways.

References Cited by the Examiner UNITED STATES PATENTS 1,184,813 5/1916 Birdsall 220-23 1,695,830 12/1928 Thurneyssen 220-23 2 FOREIGN PATENTS Great Britain.

HERMAN KARL SAALBACH, Primary Examiner.

Assistant Examiners. 

1. A TRAVELING WAVE ELECTRON DISCHARGE DEVICE COMPRISING AN ENVELOPE MADE OF A DEFORMABLE, METALLIC MATERIAL, MEANS FOR GENERATING AND PROJECTING AN ELECTRON BEAM, MEANS DISPOSED FOR COLLECTING SAID ELECTRON BEAM, WAVE PROPAGATING MEANS DISPOSED IN AN INTERACTING RELATIONSHIP WITH SAID ELECTRON BEAM, A PLURALITY OF ELECTRICALLY INSULATING, HEAT CONDUCTING SUPPORT MEMBERS DISPOSED BETWEEN AND ABUTTING SAID ENVELOPE AND SAID WAVE PROPAGATING MEANS TO POSITION SAID WAVE PROPAGATING MEANS IN A SPACED RELATIONSHIP WITH RESPECT TO SAID ENVELOPE, AND ANNULARLY SHAPED MEMBERS DISPOSED ABOUT SAID ENVELOPE 